JP2023038963A - Method for producing water-absorbing resin composition - Google Patents

Abstract

To provide a method for producing a new water-absorbing resin composition by utilizing a decomposed product of a crosslinked polymer included in a used water-absorbing resin composition, thereby contributing to resource savings and reduced environmental load.SOLUTION: A method for producing a water-absorbing resin composition includes a polymerization step for yielding a hydrous gel containing a crosslinked polymer (A2) by polymerizing a reactive composition that contains a reactive decomposed product and a crosslinker (b2), the reactive decomposed product being formed by decomposing a crosslinked polymer (A1) having a water-soluble vinyl monomer (a1) and a crosslinker (b1) as constitutional units by electromagnetic wave irradiation.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a method for producing a water absorbent resin composition.

As the amount of sanitary products used increases, the problem of waste disposal of used sanitary products is becoming a serious problem. Sanitary goods, especially paper diapers, have rapidly spread as indispensable goods in an age of declining birthrate and aging society, and their consumption is increasing rapidly.

Regarding waste disposal of sanitary products after use, paper diapers and the like are usually incinerated, but since the percentage of water in diapers is nearly 80%, incineration requires a large amount of combustion energy. For this reason, the treatment places a heavy load on the incinerator itself, which leads to shortening of the life of the incinerator. In addition, since incineration leads to air pollution and global warming, and is also a factor that places a burden on the environment, improvement is strongly desired.

In order to solve the above problems, studies are underway to collect and reuse members from used sanitary products. Sanitary products usually contain an absorbent body composed of pulp fibers and water-absorbent resin particles, and the pulp fibers and water-absorbent resin particles must be separated in order to reuse them as members. However, since the water-absorbing resin particles in the absorbent body of the used sanitary goods absorb water and become swollen gel state, it is difficult to separate them as they are. Therefore, a technique has been proposed to decompose and solubilize the water-absorbent resin particles and separate the solubilized components of the pulp fibers and the water-absorbent resin particles. There is a technique (Patent Documents 1 and 2) in which pulp fibers are recovered after decomposing and solubilizing water-absorbent resin particles by treatment with a contained aqueous solution. In addition, as a technique for decomposing and solubilizing water-absorbing resin particles, a technique using an oxidizing agent such as hydrogen peroxide as a decomposition method, and a method of irradiating electromagnetic waves (Patent Documents 3 to 6) are known. .

Japanese Unexamined Patent Application Publication No. 2016-881 JP 2017-209675 A JP-A-4-317784 JP-A-6-313008 JP 2003-321574 A US Patent No. 2021-54164

The purpose of the recycling technology for used sanitary products mentioned above is to collect pulp fibers and use them as recycled pulp. In most cases, it is not sufficient from the viewpoint of recycling.

There is also an example of decomposition of water-absorbing resin particles into acrylic acid, which is a monomer component thereof, by microwave irradiation. do not have.

An object of the present invention is to produce a new water-absorbing resin composition using a decomposition product of a crosslinked polymer contained in the water-absorbing resin composition, thereby contributing to resource saving and environmental load reduction. The object is to provide a method for producing the composition.

The present invention
a reactive decomposition product obtained by irradiating a crosslinked polymer (A1) having a water-soluble vinyl monomer (a1) and a crosslinking agent (b1) as constituent units with an electromagnetic wave to decompose the crosslinked polymer (A1); A method for producing a water-absorbing resin composition, comprising a polymerization step of polymerizing a reactive composition containing a cross-linking agent (b2) to obtain a hydrous gel containing a cross-linked polymer (A2).

In addition, the present invention
A crosslinked polymer (A3) by polymerizing a monomer composition containing a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) that becomes the water-soluble vinyl monomer (a1) by hydrolysis and a crosslinking agent (b2) A polymerization step of obtaining a hydrous gel containing
A shredding step of shredding the hydrous gel to obtain a particulate hydrous gel;
and a surface cross-linking step of surface-crosslinking the water-containing gel obtained in the shredding step,
In the shredding step, the crosslinked polymer (A1) having the water-soluble vinyl monomer (a1) and the crosslinking agent (b1) as structural units is irradiated with electromagnetic waves to decompose the crosslinked polymer (A1). A method for producing a water-absorbent resin composition, wherein the reactive decomposition product is kneaded with the hydrous gel.

According to the present invention, a water absorbent resin that can contribute to resource saving and environmental load reduction by producing a new water absorbent resin composition using a decomposition product of a crosslinked polymer contained in the water absorbent resin composition. A method of making the composition can be provided.

<First embodiment>
The method for producing the water absorbent resin composition of the first embodiment includes:
a reactive decomposition product obtained by irradiating a crosslinked polymer (A1) having a water-soluble vinyl monomer (a1) and a crosslinking agent (b1) as constituent units with an electromagnetic wave to decompose the crosslinked polymer (A1); and a polymerization step of polymerizing a reactive composition containing the cross-linking agent (b2) to obtain a hydrous gel containing the cross-linked polymer (A2).

According to the method for producing a water absorbent resin composition of the first embodiment, by producing a new water absorbent resin composition using the decomposition product of the crosslinked polymer contained in the water absorbent resin composition, It is possible to provide a method for producing a water-absorbent resin composition that can contribute to reducing environmental burden.

[Polymerization process]
[Reactive composition]
(reactive decomposition product)
The reactive decomposition product is obtained by irradiating a crosslinked polymer (A1) having a water-soluble vinyl monomer (a1) and a crosslinking agent (b1) as constituent units with electromagnetic waves to decompose the crosslinked polymer (A1). be done.

The water-soluble vinyl monomer (a1) is not particularly limited, and known monomers, for example, at least one water-soluble substituent and an ethylenically unsaturated group disclosed in paragraphs 0007 to 0023 of Japanese Patent No. 3648553 and vinyl monomers (e.g., anionic vinyl monomers, nonionic vinyl monomers and cationic vinyl monomers), anionic vinyl monomers disclosed in paragraphs 0009 to 0024 of JP-A-2003-165883, nonionic vinyl At least selected from the group consisting of monomers and cationic vinyl monomers and carboxy groups, sulfo groups, phosphono groups, hydroxyl groups, carbamoyl groups, amino groups and ammonio groups disclosed in paragraphs 0041 to 0051 of JP-A-2005-75982 Vinyl monomers having one can be used.

Among these, an anionic vinyl monomer, a carboxy (salt) group, a sulfo (salt) group, an amino group, a carbamoyl group, an ammonio group, or a mono-, di- or tri-alkylammonio is preferable from the viewpoint of absorption performance. a vinyl monomer having a group, more preferably a vinyl monomer having a carboxy (salt) group or a carbamoyl group, more preferably (meth)acrylic acid (salt) and (meth)acrylamide, particularly preferably (meth)acrylic acid (salts), acrylic acid (salts) is particularly preferred.

In addition, "carboxy (salt) group" means "carboxy group" or "carboxylate group", and "sulfo (salt) group" means "sulfo group" or "sulfonate group". (Meth)acrylic acid (salt) means acrylic acid, acrylate, methacrylic acid or methacrylate, and (meth)acrylamide means acrylamide or methacrylamide. Examples of salts include alkali metal (lithium, sodium, potassium, etc.) salts, alkaline earth metal (magnesium, calcium, etc.) salts, ammonium (NH ₄ ) salts, and the like. Among these salts, alkali metal salts and ammonium salts are preferable, alkali metal salts are more preferable, and sodium salts are particularly preferable, from the viewpoint of absorption performance and the like.

The cross-linking agent (b1) is not particularly limited and is known (for example, a cross-linking agent having two or more ethylenically unsaturated groups disclosed in paragraphs 0031 to 0034 of Japanese Patent No. 3648553, a water-soluble substituent and a A cross-linking agent having at least one functional group capable of reacting with at least one ethylenically unsaturated group and a cross-linking agent having at least two functional groups capable of reacting with a water-soluble substituent, JP-A-2003-165883 A cross-linking agent having two or more ethylenically unsaturated groups, a cross-linking agent having an ethylenically unsaturated group and a reactive functional group, and a cross-linking having two or more reactive substituents disclosed in paragraphs 0028 to 0031 of the publication crosslinkable vinyl monomers disclosed in paragraph 0059 of JP-A-2005-75982 and crosslinkable vinyl monomers disclosed in paragraphs 0015-0016 of JP-A-2005-95759). can.

The crosslinked polymer (A1) is generally contained in the water-absorbent resin composition, which is a component of sanitary goods, together with pulp fibers. Examples of sanitary products include paper diapers, sanitary napkins, incontinence products, and pet sheets. The method for producing the sanitary goods is the same as the known ones (described in JP-A-2003-225565, JP-A-2006-131767, JP-A-2005-097569, etc.). The sanitary goods may be used or unused.

When the crosslinked polymer (A1) is irradiated with an electromagnetic wave, the water absorbent resin composition containing the crosslinked polymer (A1) is irradiated with the electromagnetic wave after the water absorbent resin composition is separated from the sanitary goods. Alternatively, the sanitary goods may be irradiated with electromagnetic waves without separating the water absorbent resin composition from the sanitary goods. From the viewpoint of degradability of the crosslinked polymer (A1), it is preferable to irradiate the water absorbent resin composition with electromagnetic waves after separating the water absorbent resin composition from the sanitary goods.

Separation of the water absorbent resin composition from sanitary goods can be performed by a known method. As a known method for separating the water absorbent resin composition from sanitary goods, for example, in order to recover pulp from used diapers, an aqueous sodium hypochlorite solution and an aqueous potassium permanganate solution are used to absorb water. A method of water solubilization by breaking the bond of the resin composition (JP 2021-001783), a method of using a decomposing agent containing periodate (JP 2001-316519), using an alkaline aqueous solution (JP 2020-049398), and by using an acid such as citric acid as an inactivating aqueous solution, the neutralized portion in the water-absorbing resin composition is converted to an unneutralized state. A method of converting and promoting separation from the pulp (JP 2019-085686), putting the pulverized diaper in a tank containing water, and utilizing the difference in specific gravity and sedimentation speed between the pulp and the water absorbent resin composition. A separation method (Japanese Unexamined Patent Application Publication No. 2002-273731) can also be mentioned.

The electromagnetic wave with which the water absorbent resin composition is irradiated is not particularly limited as long as it can decompose and depolymerize the crosslinked polymer (A1). Microwaves can be exemplified as the electromagnetic waves.

The water-absorbent resin composition is a crosslinked product and retains water, but is depolymerized by selectively cutting specific bonds of the crosslinked polymer (A1) by irradiation with electromagnetic waves. In the case of decomposition by chemical or physical forces such as conventional strong alkaline substances, the bonds that are mainly cut are limited such as carbon-oxygen bonds, and carbon-carbon bonds are not actively cut. Since the main chain portion of the crosslinked polymer (A1) is not sufficiently decomposed, it is difficult to decompose into oligomers. On the other hand, in the decomposition by electromagnetic wave irradiation of the present application, specific bonds can be selectively cleaved, so the molecular weight of the reactive decomposition product produced by depolymerization can be easily controlled. Then, the reactive decomposition products produced by the depolymerization are dissolved or suspended in the water retained in the water-absorbing resin composition before irradiation.

From the viewpoint of decomposition efficiency and reuse of reactive decomposition products, the amount of water contained in the water absorbent resin composition irradiated with electromagnetic waves is preferably 20% by weight or more based on the weight of the water absorbent resin composition, and reactivity From the viewpoint of reuse of decomposition products, the content is preferably 500% by weight or less, more preferably 400% by weight or less. When the water content is 500% by weight or less, the aqueous solution or suspension of the reactive decomposition product can be used without dehydration treatment when reusing the reactive decomposition product.

The output of the electromagnetic wave with which the water absorbent resin composition is irradiated is preferably 200 W or more, more preferably 500 W or more, from the viewpoint of efficiently decomposing the crosslinked polymer (A1), and from the same viewpoint, preferably 1500 W or less. , 1000 W or less.

The irradiation time of the electromagnetic wave is not particularly limited, but from the viewpoint of efficiently decomposing the crosslinked polymer (A1), it is preferably 2 minutes or more, more preferably 5 minutes or more, and from the viewpoint of economy, 120 minutes or less. Preferably, 60 minutes or less is more preferable.

The temperature of the water-absorbing resin composition when irradiating the electromagnetic wave is not particularly limited, but from the viewpoint of efficiently decomposing the crosslinked polymer (A1), it is preferably 30 ° C. or higher, more preferably 50 ° C. or higher. From the viewpoint of reuse and carbon yield, the temperature is preferably 300° C. or lower, more preferably 250° C. or lower.

From the viewpoint of efficiently decomposing the crosslinked polymer (A1), the irradiation of the water absorbent resin composition with the electromagnetic wave is preferably carried out in the presence of a radical source. Examples of the radical source include ascorbic acid and/or ascorbic acid derivatives, prooxidants, sodium hypochlorite, potassium permanganate, ozone, and hydrogen peroxide. Hydrogen peroxide is preferred from the viewpoint of economy.

Ascorbic acid and ascorbic acid derivatives are not particularly limited as long as they are known, but ascorbic acid may be any of L-, D- and DL-forms. - Ascorbic acid is preferred. An ascorbic acid derivative means ascorbic acid and a derivative obtained by chemically modifying or substituting a part thereof. Specific examples of ascorbic acid derivatives include ascorbic acid phosphate, ascorbic acid sulfate, and ascorbic acid glycoside. Metal salts (sodium, potassium, magnesium, calcium, etc.) and organic salts (ammonium, amine, etc.) of these ascorbic acid and ascorbic acid derivatives can also be used, and are included in the ascorbic acid and ascorbic acid derivatives of the present invention. . These ascorbic acid and ascorbic acid derivatives may be used alone, in combination of two or more, or in combination with iron ions, copper ions, and the like.

The reactive decomposition product of the crosslinked polymer (A1) obtained in the decomposition step is obtained as a mixture of (a1), which is the constituent monomer of the crosslinked polymer (A1), their polymers, and the like. From the viewpoint of reuse, the constituent monomers of the crosslinked polymer (A1) and the water-soluble polymers of the constituent monomers are preferred.

The number average molecular weight of the reactive decomposition product of the crosslinked polymer (A1) obtained in the decomposition step is preferably 50 or more, more preferably 70, from the viewpoint of reusing the decomposition product as a raw material for the crosslinked polymer (A2). From the viewpoint of reaction efficiency when reacting with a monomer or oligomer, it is preferably 500,000 or less, more preferably 100,000 or less, and particularly preferably 10,000 or less. In this specification, the number average molecular weight of the reactive decomposition product of the crosslinked polymer (A1) obtained in the decomposition step is measured by the method described in Examples.

The reactive composition may contain, in addition to the reactive decomposition products, other vinyl monomers copolymerizable with the reactive decomposition products. Examples of the other vinyl monomers include the water-soluble vinyl monomer (a1) and the vinyl monomer (a2) that becomes the water-soluble vinyl monomer (a1) by hydrolysis [hereinafter also referred to as vinyl monomer (a2). ] and other vinyl monomers (a3) copolymerizable therewith.

The vinyl monomer (a2) is not particularly limited, and is known {for example, a vinyl monomer having at least one hydrolyzable substituent that becomes a water-soluble substituent by hydrolysis disclosed in paragraphs 0024 to 0025 of Japanese Patent No. 3648553. monomer, at least one hydrolyzable substituent [1,3-oxo-2-oxapropylene (-CO-O-CO-) group disclosed in paragraphs 0052 to 0055 of JP-A-2005-75982, Acyl group, cyano group, etc.] can be used.

The water-soluble vinyl monomer means a vinyl monomer that dissolves at least 100 g in 100 g of water at 25°C. In addition, the hydrolyzability of the vinyl monomer (a2) means the property of being hydrolyzed by the action of water and, if necessary, a catalyst (acid, base, etc.) to become water-soluble. Hydrolysis of the vinyl monomer (a2) may be performed during polymerization, after polymerization, or at both of these times, but is preferably performed after polymerization from the viewpoint of the absorption performance of the resulting water-absorbing resin composition.

When the reactive composition contains the water-soluble vinyl monomer (a1) and/or the vinyl monomer (a2), the content of the water-soluble vinyl monomer (a1) and the content of the vinyl monomer (a2) The content of the reactive decomposition product with respect to the total 100 parts by mass of is preferably 1 part by mass or more, more preferably 5 parts by mass or more, from the viewpoint of recycling efficiency, and preferably 70 parts by mass or less from the viewpoint of water absorption performance. 50 parts by mass or less is more preferable.

The vinyl monomer (a3) is not particularly limited, and is known (for example, hydrophobic vinyl monomers disclosed in paragraphs 0028 to 0029 of Japanese Patent No. 3648553; 2005-75982, paragraph 0058) can be used, and specifically, vinyl monomers (i) to (iii) below can be used.
(i) Aromatic ethylenic monomer having 8 to 30 carbon atoms Styrene such as styrene, α-methylstyrene, vinyltoluene and hydroxystyrene, vinylnaphthalene, and halogen-substituted styrene such as dichlorostyrene.
(ii) Aliphatic ethylenic monomers having 2 to 20 carbon atoms Alkenes (ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.); and alkadienes (butadiene, isoprene, etc.).
(iii) C5-C15 alicyclic ethylenic monomers monoethylenically unsaturated monomers (pinene, limonene, indene, etc.); and polyethylene vinyl monomers [cyclopentadiene, bicyclopentadiene, ethylidenenorbornene, etc.], and the like.

The ratio (mol%) of the amount of the vinyl monomer (a3) to the sum of the amounts of the reactive decomposition products and other vinyl monomers in the reactive composition is 0 from the viewpoint of absorption performance and the like. is preferably from 0 to 5, more preferably from 0 to 3, particularly preferably from 0 to 2, and most preferably from 0 to 1.5. % is most preferred.

(Crosslinking agent (b2))
The cross-linking agent (b2) is not particularly limited, and the same as the cross-linking agent (b1) can be used.

The content of the cross-linking agent (b2) in the reactive composition is, from the viewpoint of absorption performance and the like, the reactive decomposition product, and when the reactive composition contains other vinyl monomers, It is preferably 0.001 to 5 mol parts, more preferably 0.005 to 1 mol part, per 100 mol parts in total of the product and other vinyl monomers.

Examples of the method for polymerizing the reactive composition include known solution polymerization and known reversed-phase suspension polymerization. Among the methods for polymerizing the reactive composition, the solution polymerization method is preferable, and the aqueous solution polymerization method is particularly preferable because it does not require the use of an organic solvent or the like and is advantageous in terms of production cost. The aqueous solution adiabatic polymerization method is most preferable because it provides a water-absorbing resin composition having a large Δ and a small amount of water-soluble components, and does not require temperature control during polymerization.

When the reactive composition is polymerized by aqueous solution polymerization, a mixed solvent containing water and an organic solvent can be used, and the organic solvent includes methanol, ethanol, acetone, methyl ethyl ketone, N,N-dimethylformamide, dimethyl Sulfoxides and mixtures of two or more thereof may be mentioned. When the reactive composition is polymerized by aqueous solution polymerization, the amount (% by weight) of the organic solvent used is preferably 40 or less, more preferably 30 or less based on the weight of water.

When a catalyst is used for polymerization, conventionally known radical polymerization catalysts can be used, for example, azo compounds [azobisisobutyronitrile, azobiscyanovaleric acid and 2,2′-azobis(2-amidinopropane) hydrochloride etc.], inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate and sodium persulfate, etc.), organic peroxides [benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, persuccinic acid oxide and di(2-ethoxyethyl) peroxydicarbonate, etc.] and redox catalysts (alkali metal sulfites or bisulfites, ammonium sulfite, ammonium bisulfite and reducing agents such as ascorbic acid and alkali metal persulfates, A combination with an oxidizing agent such as ammonium persulfate, hydrogen peroxide and organic peroxide). These catalysts may be used alone, or two or more of them may be used in combination.

The amount (% by weight) of the radical polymerization catalyst used is 0.0005 to 0.0005 based on the total weight of the reactive decomposition product and the other vinyl monomer when the other vinyl monomer is used. 5 is preferred, more preferably 0.001-2.

At the time of polymerization, a polymerization control agent such as a chain transfer agent may be used in combination as necessary. Specific examples thereof include sodium hypophosphite, sodium phosphite, alkyl mercaptan, alkyl halide, thiocarbonyl compound etc. These polymerization control agents may be used alone, or two or more of them may be used in combination.

The amount (% by weight) of the polymerization control agent used is 0.0005 to 0.0005 based on the total weight of the reactive decomposition product and the other vinyl monomer when the other vinyl monomer is used. 5 is preferred, more preferably 0.001-2.

In the polymerization step, the reactive composition is polymerized in the presence of at least one organic main group element compound selected from the group consisting of organic iodine compounds, organic tellurium compounds, organic antimony compounds and organic bismuth compounds, It is possible to improve gel strength, absorbency under load, and gel permeation speed upon water absorption.

The organic main group element compound is not limited as long as it is an organic main group element compound that functions as a dormant species for radical polymerization. /001496, organic bismuth compounds described in WO2006/062255, and the like can be used.

The amount of the organic main group element compound used is the reactive decomposition product from the viewpoint of improving the gel strength at the time of water absorption, the absorption amount under load, and the gel flow rate, and the reactive decomposition product when using the other vinyl monomer. and the other vinyl monomer, preferably 0.0005 to 0.1 wt%, more preferably 0.005 to 0.05 wt%.

When a suspension polymerization method or a reverse-phase suspension polymerization method is employed as the polymerization method, polymerization may be carried out in the presence of a conventionally known dispersant or surfactant, if necessary. In the case of the reversed-phase suspension polymerization method, the polymerization can be carried out using conventionally known hydrocarbon solvents such as xylene, normal hexane and normal heptane.

The polymerization initiation temperature can be appropriately adjusted depending on the type of catalyst used, but is preferably 0 to 100°C, more preferably 2 to 80°C.

When a solvent (organic solvent, water, etc.) is used for polymerization, it is preferred to distill off the solvent after polymerization. When the solvent contains an organic solvent, the content (% by weight) of the organic solvent after distillation is preferably 0 to 10, more preferably 0 to 5, particularly preferably 0 to 5, based on the weight of the crosslinked polymer (A2). is 0-3, most preferably 0-1. Within this range, the absorption performance of the water absorbent resin composition is further improved.

When the solvent contains water, the water content (% by weight) after distillation is preferably 0 to 20, more preferably 1 to 10, particularly preferably 2 to 9, based on the weight of the crosslinked polymer (A2). Most preferably 3-8. Within this range, the absorption performance is further improved.

A water-containing gel (hereinafter also referred to as a water-containing gel) in which the crosslinked polymer (A2) contains water can be obtained by the polymerization method described above.

When an acid group-containing monomer such as acrylic acid or methacrylic acid is used as the other vinyl monomer, the water-containing gel may be neutralized with a base. The degree of neutralization of acid groups is preferably 50 to 80 mol %. If the degree of neutralization is less than 50 mol %, the resulting hydrous gel polymer will have high adhesiveness, and workability during production and use may deteriorate. Furthermore, the water-retaining capacity of the obtained water-absorbent resin composition may decrease. On the other hand, if the degree of neutralization exceeds 80%, the resulting resin will have a high pH and may be unsafe for human skin.

The neutralization may be performed at any stage after the polymerization of the crosslinked polymer (A2) in the production of the water-absorbing resin composition. exemplified as

As the neutralizing base, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkali metal carbonates such as sodium carbonate, sodium hydrogencarbonate and potassium carbonate can usually be used.

The content and moisture of the organic solvent were measured by a heat drying moisture meter [MS-70 manufactured by A&D Co., Ltd., setting temperature: 120 ° C., setting time: 45 minutes, atmospheric temperature and humidity before heating: 25 ±2°C, 50±10% RH].

[Shredding process]
The method for producing the water-absorbent resin composition of the first embodiment may have a shredding step of shredding the hydrous gel, if necessary. The size (maximum diameter) of the gel after shredding is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, particularly preferably 1 mm to 1 cm. Within this range, the drying property in the drying step is further improved. The weight average particle size (D50) of the gel after shredding is preferably 10 μm to 5000 μm, more preferably 100 μm to 4000 μm, and particularly preferably 200 μm to 3000 μm. Within this range, the drying property in the drying step is further improved. The gel weight average particle size can be measured by the method described in WO2011/126079.

Shredding can be performed by a known method, and can be performed using a shredding device (eg, Vex mill, rubber chopper, farmer mill, mincing machine, impact pulverizer, roll pulverizer) and the like.

[Drying process]
The method for producing a water-absorbing resin composition of the first embodiment comprises drying the water-containing gel, distilling off the solvent (including water) in the water-containing gel, and absorbing water containing the crosslinked polymer (A2). You may have a drying process which obtains a resin composition.

As a drying method in the drying step, microwave drying, a thin film drying method using a drum dryer or the like, a (heating) reduced pressure drying method, a freeze drying method, a drying method using infrared rays, decantation, filtration, or the like can be applied.

The drying temperature in the drying step is 100 to 300°C, preferably 150 to 250°C. If the drying temperature is high, the drying time will be shortened, resulting in improved productivity. The color tone of the water absorbent resin composition may deteriorate. If the drying temperature is lower than 100°C, the water-absorbing resin composition cannot be sufficiently dried, resulting in a decrease in productivity.

In the drying step, the drying time is preferably within 60 minutes, more preferably within 40 minutes, from the viewpoint of suppressing changes in soluble matter while suppressing changes in color after long-term storage in a hot and humid environment. preferable. Also, the drying time is generally preferably 10 minutes or more. Short drying times can lead to undried material and clogging later in the milling process.

[Pulverization process]
In the method for producing a water absorbent resin composition of the first embodiment, the water absorbent resin composition obtained in the drying step is pulverized to obtain a particulate water absorbent resin composition containing the crosslinked polymer (A2). It may have a pulverization step to obtain

In the pulverization step, the method for pulverizing the water-absorbent resin composition containing the crosslinked polymer (A2) is not particularly limited, and a pulverizing device (e.g., hammer pulverizer, impact pulverizer, roll pulverizer, machine and jet stream type pulverizer), etc. can be used. The pulverized water absorbent resin composition can be adjusted in particle size by sieving or the like, if necessary.

[Surface cross-linking step]
The water absorbent resin composition preferably has a structure in which the surface of the crosslinked polymer (A2) is crosslinked by the surface crosslinking agent (d). By cross-linking the surface of the crosslinked polymer (A2), the gel strength of the water-absorbent resin composition can be improved, and the desired water retention capacity and the absorption capacity under load of the water-absorbent resin composition are satisfied. can be done. The surface cross-linking agent (d) can be inorganic or organic. As the surface cross-linking agent (d), known (polyvalent glycidyl compounds, polyvalent amines, polyvalent aziridine compounds and polyvalent isocyanate compounds described in JP-A-59-189103, etc., JP-A-58-180233 And the polyhydric alcohol of JP-A-61-16903, the silane coupling agent described in JP-A-61-211305 and JP-A-61-252212, the JP-A-5-508425 described Organic surface cross-linking agents such as alkylene carbonates and polyvalent oxazoline compounds described in JP-A-11-240959 can be used. Among these surface cross-linking agents (d), polyhydric glycidyl compounds, polyhydric alcohols and polyhydric amines are preferred from the viewpoint of economy and absorption properties, more preferred are polyhydric glycidyl compounds and polyhydric alcohols, and particularly preferred are polyhydric glycidyl compounds and polyhydric alcohols. are polyhydric glycidyl compounds, most preferably ethylene glycol diglycidyl ether. The surface cross-linking agent (d) may be used alone or in combination of two or more.

When the surface of the crosslinked polymer (A2) is crosslinked with the surface crosslinking agent (d), the method for producing a water-absorbing resin composition of the first embodiment includes the crosslinked polymer obtained in the drying step. It has a surface cross-linking step of surface cross-linking the water absorbent resin composition containing (A2).

The amount (% by weight) of the surface cross-linking agent (d) used is not particularly limited because it can be varied depending on the type of the surface cross-linking agent, cross-linking conditions, target performance, etc., but is not particularly limited from the viewpoint of absorption characteristics and the like. Therefore, it is preferably 0.001 to 3, more preferably 0.005 to 2, particularly preferably 0.01 to 1.5, based on the weight of the crosslinked polymer (A2).

Surface cross-linking of the cross-linked polymer (A2) can be carried out by mixing the water absorbent resin composition containing the cross-linked polymer (A2) and the surface cross-linking agent (d) and heating the mixture. The method for mixing the water absorbent resin composition containing the crosslinked polymer (A2) and the surface cross-linking agent (d) includes a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, and a Nauta mixer. mixer, double-arm kneader, fluidized mixer, V-shaped mixer, mincing mixer, ribbon mixer, fluidized mixer, airflow mixer, rotating disc mixer, conical blender, roll mixer, etc. A method of uniformly mixing the water-absorbing resin composition containing the crosslinked polymer (A2) and the surface cross-linking agent (d) using an apparatus can be mentioned. At this time, the surface cross-linking agent (d) may be diluted with water and/or any solvent before use.

The temperature at which the crosslinked polymer (A2) and the surface cross-linking agent (d) are mixed is not particularly limited, but is preferably 10 to 150°C, more preferably 20 to 100°C, and particularly preferably 25 to 80°C. .

After mixing the crosslinked polymer (A2) and the surface cross-linking agent (d), heat treatment is usually performed. The heating temperature is preferably 100 to 180°C, more preferably 110 to 175°C, particularly preferably 120 to 170°C, from the viewpoint of breakage resistance of the water absorbent resin composition. Heating at 180° C. or less enables indirect heating using steam, which is advantageous in terms of facilities. Heating temperatures below 100° C. may result in poor absorption performance. The heating time can be appropriately set depending on the heating temperature, but from the viewpoint of absorption performance, it is preferably 5 to 60 minutes, more preferably 10 to 40 minutes. It is also possible to further surface-crosslink the water-absorbing resin composition obtained by surface-crosslinking using a surface-crosslinking agent that is the same as or different from the surface-crosslinking agent used first.

After cross-linking the surface of the cross-linked polymer (A2) with the surface cross-linking agent (d), the particle size is adjusted by sieving if necessary. The average particle size of the obtained particles is preferably 100-600 μm, more preferably 200-500 μm. The content of fine particles is preferably as small as possible, the content of particles of 100 μm or less is preferably 3% by weight or less, and the content of particles of 150 μm or less is more preferably 3% by weight or less.

In addition, in the method for producing a water absorbent resin composition of the first embodiment, instead of the shredding step and the surface cross-linking step according to the first embodiment, the shredding step and the surface cross-linking step according to the second embodiment described later. It may have a cross-linking step. That is, the method for producing the water absorbent resin composition of the first embodiment includes:
a reactive decomposition product obtained by irradiating a crosslinked polymer (A1) having a water-soluble vinyl monomer (a1) and a crosslinking agent (b1) as constituent units with an electromagnetic wave to decompose the crosslinked polymer (A1); A polymerization step of polymerizing a reactive composition containing a cross-linking agent (b2) to obtain a hydrous gel containing the cross-linked polymer (A2);
A shredding step of shredding the hydrous gel to obtain a particulate hydrous gel;
and a surface cross-linking step of surface-crosslinking the water-containing gel obtained in the shredding step,
The method for producing a water-absorbing resin composition may include adding the reactive decomposition product in the shredding step.

<Second embodiment>
The method for producing the water absorbent resin composition of the second embodiment includes:
A crosslinked polymer (A3) by polymerizing a monomer composition containing a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) that becomes the water-soluble vinyl monomer (a1) by hydrolysis and a crosslinking agent (b2) A polymerization step of obtaining a hydrous gel containing
A shredding step of shredding the hydrous gel to obtain a particulate hydrous gel;
and a surface cross-linking step of surface-crosslinking the water-containing gel obtained in the shredding step,
In the shredding step, the crosslinked polymer (A1) having the water-soluble vinyl monomer (a1) and the crosslinking agent (b1) as structural units is irradiated with electromagnetic waves to decompose the crosslinked polymer (A1). The reactive decomposition product is kneaded with the hydrous gel.

According to the method for producing a water absorbent resin composition of the second embodiment, resource saving and It is possible to provide a method for producing a water-absorbent resin composition that can contribute to reducing environmental burden.

[Polymerization process]
The water-soluble vinyl monomer (a1) according to this embodiment is the same as the water-soluble vinyl monomer (a1) according to the first embodiment, so the description is omitted. The vinyl monomer (a2) according to the present embodiment is the same as the vinyl monomer (a2) according to the first embodiment, so the description is omitted. The cross-linking agent (b2) according to this embodiment can be the same as the cross-linking agent (b1) according to the first embodiment.

When either the water-soluble vinyl monomer (a1) or the vinyl monomer (a2) is used as a structural unit, each one type may be used alone as a structural unit, and two or more types may be used as a structural unit, if necessary. . The same applies to the case where the water-soluble vinyl monomer (a1) and the vinyl monomer (a2) are used as structural units. Further, when the water-soluble vinyl monomer (a1) and the vinyl monomer (a2) are used as structural units, the molar ratio [(a1)/(a2)] of these contained is preferably 75/25 to 99/1, More preferably 85/15 to 95/5, particularly preferably 90/10 to 93/7, most preferably 91/9 to 92/8. Within this range, the absorption performance is further improved.

The monomer composition includes, in addition to the water-soluble vinyl monomer (a1) and the vinyl monomer (a2), other monomers copolymerizable with the water-soluble vinyl monomer (a1) and the vinyl monomer (a2). It may contain a vinyl monomer (a4). Examples of the other vinyl monomer (a4) include those similar to the vinyl monomer (a3) according to the first embodiment.

The content of the vinyl monomer (a4) in the monomer composition is 0 based on the total number of moles of the water-soluble vinyl monomer (a1) and the vinyl monomer (a2) from the viewpoint of absorption performance and the like. to 5 mol%, more preferably 0 to 3 mol%, particularly preferably 0 to 2 mol%, and most preferably 0 to 1.5 mol%. ) unit content is most preferably 0 mol %.

The content of the cross-linking agent (b2) in the monomer composition is the sum of the water-soluble vinyl monomer (a1) and the vinyl monomer (a2), the total of the vinyl monomer (a4), and When using, it is preferably 0.001 to 5 mol parts per 100 mol parts of the total of the water-soluble vinyl monomer (a1), the vinyl monomer (a2), and the vinyl monomer (a4). 005 to 1 molar part is more preferable.

Examples of the method for polymerizing the monomer composition include known solution polymerization and known reversed-phase suspension polymerization.

Of the methods for polymerizing the monomer composition, preferred is the solution polymerization method, and particularly preferred is the aqueous solution polymerization method because it does not require the use of an organic solvent or the like and is advantageous in terms of production cost. The aqueous solution adiabatic polymerization method is most preferable because it provides a water-absorbent resin composition containing a large amount of water and a small amount of water-soluble components, and does not require temperature control during polymerization.

When the monomer composition is polymerized by aqueous solution polymerization, a mixed solvent containing water and an organic solvent can be used, and the organic solvent includes methanol, ethanol, acetone, methyl ethyl ketone, N,N-dimethylformamide, Dimethylsulfoxide and mixtures of two or more thereof may be mentioned. When the monomer composition is polymerized by aqueous solution polymerization, the amount (% by weight) of the organic solvent used is preferably 40 or less, more preferably 30 or less based on the weight of water.

When a catalyst is used for polymerization, the radical polymerization catalyst that can be used in the method for producing a water absorbent resin composition according to the first embodiment can be used.

The amount (% by weight) of the radical polymerization catalyst used is the water-soluble vinyl monomer (a1) and the vinyl monomer (a2) when using the water-soluble vinyl monomer (a1) and the vinyl monomer (a2). , and the vinyl monomer (a4), preferably 0.0005 to 5, more preferably 0.001 to 2.

At the time of polymerization, if necessary, a polymerization control agent such as a chain transfer agent that can be used in the method for producing a water absorbent resin composition according to the first embodiment may be used together.

The amount (% by weight) of the polymerization control agent used is the water-soluble vinyl monomer (a1) and the vinyl monomer (a2) when the vinyl monomer (a4) is used. , and the vinyl monomer (a4), preferably 0.0005 to 5, more preferably 0.001 to 2.

In the polymerization step, the monomer composition is polymerized in the presence of an organic main group element compound that can be used in the method for producing a water-absorbing resin composition according to the first embodiment, thereby gelling at the time of water absorption Strength, absorbency under load and gel flow rate can be improved.

The amount of the organic main group element compound used is the vinyl monomer (a4) of the water-soluble vinyl monomer (a1) and the vinyl monomer (a2) from the viewpoint of improving the gel strength at the time of water absorption, the absorption amount under load, and the gel flow rate. When using, the water-soluble vinyl monomer (a1), vinyl monomer (a2), and vinyl monomer (a4), based on the total weight, preferably 0.0005 to 0.1 wt%, more preferably 0. 005 to 0.05% by weight.

When a suspension polymerization method or a reverse-phase suspension polymerization method is employed as the polymerization method, polymerization may be carried out in the presence of a conventionally known dispersant or surfactant, if necessary. In the case of the reversed-phase suspension polymerization method, the polymerization can be carried out using conventionally known hydrocarbon solvents such as xylene, normal hexane and normal heptane.

The polymerization initiation temperature can be appropriately adjusted depending on the type of catalyst used, but is preferably 0 to 100°C, more preferably 2 to 80°C.

When a solvent (organic solvent, water, etc.) is used for polymerization, it is preferred to distill off the solvent after polymerization. When the solvent contains an organic solvent, the content (% by weight) of the organic solvent after distillation is preferably 0 to 10, more preferably 0 to 5, particularly preferably 0 to 5, based on the weight of the crosslinked polymer (A3). is 0-3, most preferably 0-1. Within this range, the absorption performance of the water absorbent resin composition is further improved.

When the solvent contains water, the water content (% by weight) after distillation is preferably 0 to 20, more preferably 1 to 10, particularly preferably 2 to 9, based on the weight of the crosslinked polymer (A3). Most preferably 3-8. Within this range, the absorption performance is further improved.

A water-containing gel-like substance (hereinafter also referred to as a water-containing gel) in which the crosslinked polymer (A3) contains water can be obtained by the polymerization method described above.

When using an acid group-containing monomer such as acrylic acid or methacrylic acid as the vinyl monomer (a4), the water-containing gel may be neutralized with a base. The degree of neutralization of acid groups is preferably 50 to 80 mol %. If the degree of neutralization is less than 50 mol %, the resulting hydrous gel polymer will have high adhesiveness, and workability during production and use may deteriorate. Furthermore, the water-retaining capacity of the obtained water-absorbent resin composition may decrease. On the other hand, if the degree of neutralization exceeds 80%, the resulting resin will have a high pH and may be unsafe for human skin.

The neutralization may be performed at any stage after the polymerization of the crosslinked polymer (A3) in the production of the water-absorbent resin composition. exemplified as

As the neutralizing base, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkali metal carbonates such as sodium carbonate, sodium hydrogencarbonate and potassium carbonate can usually be used.

[Shredding process]
The reactive decomposition product to be kneaded with the hydrous gel in the shredding step according to the second embodiment is the same as the reactive decomposition product according to the first embodiment, so the description is omitted.

The method of adding the reactive decomposition product is not particularly limited, and a method of adding the reactive decomposition product to the hydrogel, shredding the hydrogel, and kneading the hydrogel and the reactive decomposition product. and/or a method of shredding the hydrogel while adding the reactive decomposition product and kneading the reactive decomposition product and the hydrogel. Further, after shredding the hydrous gel, after adding the reactive decomposition product and/or while adding the reactive decomposition product, the hydrous gel is further shredded, so that the hydrous gel and the reactive The method of kneading the decomposition product is also included in the method of adding the reactive decomposition product in the shredding step.

Also, the reactive decomposition product may be added simultaneously with water and/or the solvent. When a reactive decomposition product is added simultaneously with water and/or a solvent, a solution or suspension of the reactive decomposition product can be added, and from the viewpoint of workability, etc., it is preferable to add an aqueous solution or a water suspension. , more preferably an aqueous suspension. When adding a suspension, it is preferably added by spraying or dropwise.

The amount of the reactive decomposition product added in the shredding step according to the second embodiment is preferably 1 part or more with respect to 100 parts by weight of the crosslinked polymer (A1) from the viewpoint of recycling efficiency, and 5 parts by weight. Part or more is more preferable, and from the viewpoint of water absorption performance, 70 parts by weight or less is preferable, and 50 parts by weight or less is more preferable.

Methods for kneading the hydrous gel and the reactive decomposition product include a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, a Nauta mixer, a double-arm kneader, a fluid mixer, Using a mixing device such as a V-type mixer, a mincing mixer, a ribbon-type mixer, a fluidized mixer, an airflow-type mixer, a rotating disk-type mixer, a conical blender, and a roll mixer, the hydrous gel and the reactive decomposition are and a method of uniformly mixing substances.

Other conditions of the shredding process according to the second embodiment are the same as those of the shredding process according to the first embodiment, so description thereof is omitted.

[Drying process]
The method for producing a water-absorbing resin composition of the second embodiment includes drying the water-containing gel, distilling off the solvent (including water) in the water-containing gel, and water-absorbing water containing the crosslinked polymer (A3). You may have a drying process which obtains a resin composition. The drying process according to this embodiment is the same as the drying process according to the first embodiment, so the description is omitted.

[Pulverization process]
In the method for producing a water absorbent resin composition of the present embodiment, the water absorbent resin composition obtained in the drying step is pulverized to obtain a particulate water absorbent resin composition containing the crosslinked polymer (A3). It may have a pulverization step. The pulverization process according to the present embodiment is the same as the pulverization process according to the first embodiment, so the description is omitted.

[Surface cross-linking step]
The reactive decomposition product added in the shredding step of the second embodiment is crosslinked with the crosslinked polymer (A3) by the crosslinked polymer (d). By cross-linking, the reactive decomposition products are not eluted again, and even when the cross-linked polymer (A3) absorbs water and changes to a gel state, gel strength is maintained by having a cross-linked structure. The surface cross-linking agent (d) that can be used in the method for producing the water absorbent resin composition of the second embodiment is the same as the surface cross-linking agent (d) that can be used in the first embodiment, so the description is omitted. .

The amount (% by weight) of the surface cross-linking agent (d) used is not particularly limited because it can be varied depending on the type of the surface cross-linking agent, cross-linking conditions, target performance, etc., but is not particularly limited from the viewpoint of absorption characteristics and the like. Therefore, based on the total weight of the reactive decomposition product and the crosslinked polymer (A3), it is preferably 0.001 to 3, more preferably 0.005 to 2, and particularly preferably 0.01 to 1.5. be.

The method and conditions for surface cross-linking in the surface cross-linking step are the same as the method and conditions for surface cross-linking in the surface cross-linking step according to the first embodiment, and thus description thereof is omitted.

After cross-linking the reactive decomposition product and the cross-linked polymer (A3) with the surface cross-linking agent (d), the particle size is adjusted by sieving if necessary. The average particle size of the obtained particles is preferably 100-600 μm, more preferably 200-500 μm. The content of fine particles is preferably as small as possible, the content of particles of 100 μm or less is preferably 3% by weight or less, and the content of particles of 150 μm or less is more preferably 3% by weight or less.

<Water absorbent resin composition>
The water absorbent resin composition obtained by the production method of the first embodiment and the production method of the second embodiment contains some other components such as residual solvent and residual cross-linking components within a range that does not impair its performance. But it's okay.

Other examples of the other components include preservatives, antifungal agents, antibacterial agents, ultraviolet absorbers, antioxidants, colorants, fragrances, deodorants, liquid permeability improvers, inorganic powders and organic fibers. and the like. The amount is usually 5% by weight or less based on the weight of the water absorbent resin composition.

Although the shape of the water absorbent resin composition is not particularly limited, it is preferably particulate from the viewpoint of improving the absorption performance. The weight average particle diameter (μm) of the particulate water absorbent resin composition (hereinafter also referred to as water absorbent resin composition particles) is preferably 250 to 600, more preferably 300 to 500, and still more preferably 340. ~460. When the weight-average particle size is less than 250 µm, the liquid permeability deteriorates, and when it exceeds 600 µm, the absorption speed deteriorates.

In addition, the weight average particle size was measured using a low-tap test sieve shaker and a standard sieve (JISZ8801-1:2006), Perry's Chemical Engineers Handbook 6th Edition (McGraw-Hill Book Company, 1984, page 21). That is, JIS standard sieves of 1000 μm, 850 μm, 710 μm, 500 μm, 425 μm, 355 μm, 250 μm, 150 μm, 125 μm, 75 μm and 45 μm and a saucer are combined in this order from the top. About 50 g of the particles to be measured are placed in the top sieve and shaken for 5 minutes with a Rotap test sieve shaker. The weight of the particles to be measured on each sieve and the tray is weighed, the total is 100% by weight, and the weight fraction of the particles on each sieve is obtained. ) and the weight fraction on the vertical axis], draw a line connecting the points, determine the particle diameter corresponding to a weight fraction of 50% by weight, and take this as the weight average particle diameter.

Since the smaller the content of the fine powder contained in the water absorbent resin composition particles, the better the liquid permeability, the water absorbent resin composition having a particle diameter of less than 150 μm in the total weight of all the water absorbent resin composition particles. The weight percentage (% by weight) of the particles is 3 or less, preferably 1 or less. The weight ratio of the water-absorbent resin composition particles having a particle size of less than 150 μm can be determined using the graph created when determining the weight average particle size.

The shape of the water-absorbent resin composition particles is not particularly limited, and examples thereof include irregular crushed shape, scaly shape, pearl-like shape, and rice grain-like shape. Of these, irregularly crushed forms are preferred from the viewpoints of good entanglement with fibrous materials for use in paper diapers and the like, and no fear of falling off from fibrous materials.

The water absorbent resin composition contains the crosslinked polymer (A2) and/or the crosslinked polymer (A3). Further, the water absorbent resin composition may contain the crosslinked polymer (A1) in addition to the crosslinked polymer (A2) and the crosslinked polymer (A3). The total content of the crosslinked polymers (A1) to (A3) in the water absorbent resin composition is preferably 50% by weight or more, and 60% by weight, from the viewpoint of obtaining a water absorbent resin composition having sufficient water retention capacity. % or more is more preferable. The total content of the crosslinked polymers (A1) to (A3) in the water absorbent resin composition is preferably 99.5% by weight or less, more preferably 99% by weight or less.

The water retention capacity (g/g) of the water absorbent resin composition is preferably 25 or more, more preferably 28 or more, and particularly preferably 32 or more, from the viewpoint of absorption capacity. Moreover, the upper limit is preferably 60 or less, more preferably 55 or less, and particularly preferably 50 or less, from the viewpoint of stickiness. The amount of water retention can be appropriately adjusted by the amount (% by weight) of the cross-linking agent (b2) and the surface cross-linking agent (d) used. The water retention capacity (g/g) of the water absorbent resin composition can be measured by the method described in Examples.

The absorbency under load (g/g) of the water absorbent resin composition is preferably 10 or more, more preferably 15 or more, and particularly preferably 20 or more, from the viewpoint of the absorbency of the diaper under load. . It is empirically known that the absorbency under load conflicts with the water retention capacity, and there are cases where a high water retention capacity is required and cases where a high absorption capacity under load is required depending on the configuration of the diaper. The absorbency under load (g/g) of the water absorbent resin composition can be measured by the method described in Examples.

The soluble content (% by weight) of the water absorbent resin composition is preferably less than 20%, more preferably less than 15%, relative to the water absorbent resin composition, from the viewpoint of liquid permeability and water absorption rate. If the soluble content exceeds 20%, the soluble content will be eluted at the time of water absorption, resulting in gel blocking and adversely affecting liquid permeability and water absorption capacity, which is undesirable. The soluble content (% by weight) of the water absorbent resin composition can be measured by the method described in Examples.

<Absorber>
An absorbent body can be obtained using the water absorbent resin composition. As the absorbent, the water absorbent resin composition may be used alone, or may be used together with other materials to form an absorbent. Such other materials include fibrous materials and the like. The structure and manufacturing method of the absorbent when used with fibrous materials are the same as those of known ones (Japanese Patent Laid-Open Nos. 2003-225565, 2006-131767 and 2005-097569). be.

Cellulose fibers, organic synthetic fibers, and mixtures of cellulosic fibers and organic synthetic fibers are preferable as the fibrous material.

Examples of cellulosic fibers include natural fibers such as fluff pulp, and cellulosic chemical fibers such as viscose rayon, acetate and cupra. The raw material (softwood, hardwood, etc.), manufacturing method (chemical pulp, semi-chemical pulp, mechanical pulp, CTMP, etc.), bleaching method, and the like of this cellulose-based natural fiber are not particularly limited.

Examples of organic synthetic fibers include polypropylene fibers, polyethylene fibers, polyamide fibers, polyacrylonitrile fibers, polyester fibers, polyvinyl alcohol fibers, polyurethane fibers, and heat-fusible composite fibers (the above fibers having different melting points). (sheath-and-core type, eccentric type, side-by-side type, etc.), fibers obtained by blending at least two of the above fibers, and fibers obtained by modifying the surface layer of the above fibers.

Among these fibrous materials, cellulosic natural fibers, polypropylene fibers, polyethylene fibers, polyester fibers, heat-fusible conjugate fibers and mixed fibers thereof are preferred, and more preferred are fluff pulp, heat-fusible conjugate fibers and mixed fibers thereof in that they are excellent in shape retention after water absorption by the water absorbing agent.

The length and thickness of the above-mentioned fibrous material are not particularly limited, and a length of 1 to 200 mm and a thickness of 0.1 to 100 denier can be suitably used. The shape is not particularly limited as long as it is fibrous, and examples include a thin cylindrical shape, a split yarn shape, a staple shape, a filament shape, a web shape, and the like.

When the water absorbent resin composition particles are used as an absorber together with fibrous materials, the weight ratio of the water absorbent resin composition particles and fibers (weight of water absorbent resin composition particles/weight of fibrous materials) is 40/ It is preferably 60 to 95/5, more preferably 50/50 to 90/10.

<Absorbent article>
An absorbent article can be obtained using the water absorbent resin composition. Specifically, the absorber described above is used. Absorbent products include not only sanitary goods such as paper diapers and sanitary napkins, but also anti-condensation agents, water retention agents for agriculture and gardening, waste blood solidification agents, disposable body warmers, etc. It can be applied for various uses such as retention agent use and gelling agent use. The manufacturing method of the absorbent article and the like are the same as those known (described in JP-A-2003-225565, JP-A-2006-131767, JP-A-2005-097569, etc.).

EXAMPLES The present invention will be further described with reference to Examples and Comparative Examples below, but the present invention is not limited to these. Hereinafter, unless otherwise specified, parts indicate parts by weight and % indicates % by weight. The number average molecular weight of decomposition products was measured by the following method.

<Number average molecular weight of reactive decomposition products>
As a method for measuring the number average molecular weight of the reactive decomposition product, for example, gel permeation chromatography (manufactured by Agilent Technologies, Inc.; 1200 series) (hereinafter abbreviated as GPC-MALS), an aqueous solution containing 0.5 M acetic acid and 0.2 M sodium nitrate was used as the solvent, the sample concentration was 0.2% by weight, and the column stationary phase was A polymer packing material (OHpak SB-806M HQ manufactured by Shoko Scientific Co., Ltd.) is used, and the column temperature is measured at 40°C.

<Production Example 1>
157 parts of water-soluble vinyl monomer (a1) {acrylic acid}, 0.6305 parts of internal cross-linking agent (b) {pentaerythritol triallyl ether} and 344.7 parts of deionized water were kept at 3°C while stirring and mixing. . After nitrogen was introduced into this mixture to make the dissolved oxygen content 1 ppm or less, 0.63 parts of a 1% aqueous hydrogen peroxide solution, 1.1774 parts of a 2% ascorbic acid aqueous solution and 2% 2,2'-azobis [ 2-Methyl-N-(2-hydroxyethyl)-propionamide] aqueous solution (2.355 parts) was added and mixed to initiate polymerization. After the temperature of the mixture reached 90° C., the mixture was polymerized at 90±2° C. for about 5 hours to obtain hydrous gel (1).

Next, 128.4 parts of a 48.5% sodium hydroxide aqueous solution was added to 502.3 parts of this hydrous gel (1) while being finely chopped with a mincing machine, followed by mixing. Subsequently, using a mincing machine with a perforated plate diameter of 16 mm (12VR-400K manufactured by ROYAL), after kneading and shredding four times, it was dried with a ventilated band dryer {150 ° C., wind speed 2 m / sec} to obtain a dried body. . The dried product was pulverized with a juicer mixer (Osterizer Blender manufactured by Oster), and then adjusted to a particle size range of 710 to 150 μm in opening to obtain dried product particles. The weight-average particle size of the dry particles at this time was 392 μm. 5.00 parts of a 2% water/methanol mixed solution of ethylene glycol diglycidyl ether (water/methanol weight ratio = 70/30) was added to 100 parts of the dried particles while being stirred at high speed and mixed. , and allowed to stand at 150°C for 30 minutes for surface cross-linking to obtain a water absorbent resin composition (R-1).

1.000 parts of the water-absorbent resin composition (R-1) was weighed into a test tube for decomposition, then 8.986 parts of ultrapure water was completely absorbed, left to stand for 60 minutes, and then hydrogen peroxide (35% 0.014 part of an aqueous solution (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, the lid of the test tube was closed, and microwave irradiation was performed under the following conditions. That is, the output of microwave irradiation is 500 W, the temperature is raised from room temperature to 200 ° C. for 5 minutes, and then the temperature is automatically maintained at 200 ° C. for 5 minutes to perform reactive decomposition. A product (Z-1) was obtained.

<Example 1>
152.4 parts of acrylic acid, 0.550 parts of cross-linking agent (b) {pentaerythritol triallyl ether}, 548.9 parts of deionized water, and 45.7 parts of reactive decomposition product (Z-1) are stirred and mixed. was kept at 3°C. After nitrogen was introduced into this mixture to make the dissolved oxygen content 1 ppm or less, 0.63 parts of a 1% aqueous hydrogen peroxide solution, 1.1774 parts of a 2% ascorbic acid aqueous solution, and 2% 2,2'-azobis [ 2-Methyl-N-(2-hydroxyethyl)-propionamide] aqueous solution (2.355 parts) was added and mixed to initiate polymerization. After the temperature of the mixture reached 63° C., the mixture was polymerized at 63±2° C. for about 5 hours to obtain hydrous gel (1). Next, 125.60 parts of a 48.5% aqueous sodium hydroxide solution was added to 751.8 parts of this hydrous gel (1) and mixed with a mincing machine to obtain hydrous gel particles. Further, the hydrous gel particles were dried with a ventilated band dryer {150° C., wind speed 2 m/sec} to obtain a dry product. After pulverizing the dried product with a juicer mixer, the dried product particles (1) were obtained by adjusting the particle size to a range of 710 to 150 μm in opening. While stirring 100 parts of the dried particles (1) at high speed, 7.00 parts of a 2% water/methanol mixed solution of ethylene glycol diglycidyl ether (weight ratio of water/methanol = 70/30) was sprayed. In addition, they were mixed and allowed to stand at 150° C. for 30 minutes for surface cross-linking to obtain a water absorbent resin composition (P-1).

<Example 2>
In Example 1, the same operation as in Example 1 was performed except that 548.9 parts of deionized water was changed to 491.1 parts and 45.7 parts of reactive decomposition product (Z-1) was changed to 152.4 parts. to obtain a water absorbent resin composition (P-2) of the present invention.

<Example 3>
In Example 1, the same operation as in Example 1 was performed except that 548.9 parts of deionized water was changed to 173.5 parts and 45.7 parts of reactive decomposition product (Z-1) was changed to 762.0 parts. to obtain a water absorbent resin composition (P-3) of the present invention.

<Example 4>
In Example 1, the same operation as in Example 1 was performed except that 548.9 parts of deionized water was changed to 12.7 parts and 45.7 parts of reactive decomposition product (Z-1) was changed to 1066.8 parts. to obtain a water absorbent resin composition (P-4) of the present invention.

<Example 5>
152.4 parts of acrylic acid, 0.550 parts of cross-linking agent (b) {pentaerythritol triallyl ether} and 548.9 parts of deionized water were kept at 3° C. while stirring and mixing. After nitrogen was introduced into this mixture to make the dissolved oxygen content 1 ppm or less, 0.63 parts of a 1% aqueous hydrogen peroxide solution, 1.1774 parts of a 2% ascorbic acid aqueous solution and 2% 2,2'-azobis [ 2-Methyl-N-(2-hydroxyethyl)-propionamide] aqueous solution (2.355 parts) was added and mixed to initiate polymerization. After the temperature of the mixture reached 63° C., the mixture was polymerized at 63±2° C. for about 5 hours to obtain hydrous gel (1). Next, 45.7 parts of reactive decomposition product (Z-1) and 125.60 parts of 48.5% sodium hydroxide aqueous solution were added while shredding 706.0 parts of this hydrous gel (1) with a mincing machine. to obtain hydrous gel particles. Further, the hydrous gel particles were dried with a ventilated band dryer {150° C., wind speed 2 m/sec} to obtain a dry product. After pulverizing the dried product with a juicer mixer, the dried product particles (1) were obtained by adjusting the particle size to a range of 710 to 150 μm in opening. While stirring 100 parts of the dried particles (1) at high speed, 7.00 parts of a 2% water/methanol mixed solution of ethylene glycol diglycidyl ether (weight ratio of water/methanol = 70/30) was sprayed. In addition, they were mixed and allowed to stand at 150° C. for 30 minutes for surface cross-linking to obtain a water absorbent resin composition (P-5) of the present invention.

<Comparative Example 1>
The water absorbent resin composition (R-1) obtained in Production Example 1 was used as a water absorbent resin composition for comparison.

<Comparative Example 2>
152.4 parts of acrylic acid, 0.550 parts of cross-linking agent (b) {pentaerythritol triallyl ether} and 548.9 parts of deionized water were kept at 3° C. while stirring and mixing. After nitrogen was introduced into this mixture to make the dissolved oxygen content 1 ppm or less, 0.63 parts of a 1% aqueous hydrogen peroxide solution, 1.1774 parts of a 2% ascorbic acid aqueous solution and 2% 2,2'-azobis [ 2-Methyl-N-(2-hydroxyethyl)-propionamide] aqueous solution (2.355 parts) was added and mixed to initiate polymerization. After the temperature of the mixture reached 63° C., the mixture was polymerized at 63±2° C. for about 5 hours to obtain hydrous gel (1). Next, 125.60 parts of a 48.5% aqueous sodium hydroxide solution was added to and mixed with 706.0 parts of this hydrous gel (1) while shredding it with a mincing machine to obtain hydrous gel particles. Further, the hydrous gel particles were dried with a ventilated band dryer {150° C., wind speed 2 m/sec} to obtain a dry product. After pulverizing the dried product with a juicer mixer, the dried product particles (1) were obtained by adjusting the particle size to a range of 710 to 150 μm in opening. 7.00 parts of a 2% water/methanol mixed solution of ethylene glycol diglycidyl ether (water/methanol weight ratio = 70/30) and a reactive decomposition product were added to 100 parts of the dried particles (1) while stirring at high speed. 45.7 parts of (Z-1) were added while spraying and mixed, and allowed to stand at 150° C. for 30 minutes for surface cross-linking to obtain a water absorbent resin composition (R-2) for comparison.

<Evaluation method>
[Method for measuring water retention capacity of water absorbent resin composition]
1.00 g of a water-absorbing resin composition was placed in a tea bag (20 cm long, 10 cm wide) made of nylon mesh with an opening of 63 μm (JIS Z8801-1: 2006), and physiological saline (salt concentration 0.9%) 1 ,000 ml without stirring for 1 hour, then taken out and hung for 15 minutes to drain. After that, the whole tea bag was placed in a centrifuge and dehydrated by centrifugation at 150 G for 90 seconds to remove excess physiological saline. The physiological saline used and the temperature of the measurement atmosphere were 25°C ± 2°C.
Water retention amount of the water absorbent resin composition (g / g) = (h1) - (h2)
In addition, (h2) is the weight of the tea bag measured by the same operation as above without the measurement sample.

[Method for measuring absorption under load of water absorbent resin composition]
In a cylindrical plastic tube (inner diameter: 25 mm, height: 34 mm) with a mesh opening of 63 μm (JIS Z8801-1: 2006) attached to the bottom, 250 to 500 μm using a 30 mesh sieve and a 60 mesh sieve. 0.16 g of the water-absorbing resin composition sieved to the range is weighed, and the cylindrical plastic tube is set vertically so that the measurement sample has a substantially uniform thickness on the nylon net. A weight (weight: 200.0 g, outer diameter: 24.5 mm) was put on it. After measuring the weight (M1) of the entire cylindrical plastic tube, the water-absorbing resin composition and the weight were placed in a petri dish (diameter: 12 cm) containing 60 ml of physiological saline (salt concentration: 0.9%). A cylindrical plastic tube was set up vertically, immersed with the nylon mesh side down, and allowed to stand for 60 minutes. After 60 minutes, pull up the cylindrical plastic tube from the petri dish, tilt it obliquely, collect the water adhering to the bottom in one place and drop it as water droplets to remove excess water, and then add the water-absorbent resin composition and the weight. The weight (M2) of the entire cylindrical plastic tube containing the was weighed, and the absorption under load was obtained from the following formula. The physiological saline used and the temperature of the measurement atmosphere were 25°C ± 2°C.
Absorption amount under load (g/g) of water absorbent resin composition = {(M2) - (M1)}/0.16

Table 1 shows the evaluation results.

As is clear from the results shown in Table 1, the water absorbent resin composition obtained by the production method of the present invention using the electromagnetic decomposition product of the water absorbent resin composition shown in the example is shown in the comparative example. It can be seen that both water retention capacity and absorption capacity under load are superior to the water absorbent resin composition obtained by adding the decomposed product in the process after the surface cross-linking. Moreover, even when comparing Comparative Example 1, in which no decomposed product of the water absorbent resin composition was added, with the examples of the present application, it can be seen that the absorption characteristics are the same.

From this result, the present invention can add the decomposition product of the water-absorbent resin composition, which is a waste of the water-absorbent resin composition, to the step before the surface cross-linking step and reuse it as a raw material. Since the resin composition exhibits good absorption properties, it can be said that the production method is efficient from the viewpoint of resource saving and environmental load reduction.

Claims (7)

a reactive decomposition product obtained by irradiating a crosslinked polymer (A1) having a water-soluble vinyl monomer (a1) and a crosslinking agent (b1) as constituent units with an electromagnetic wave to decompose the crosslinked polymer (A1); A method for producing a water-absorbent resin composition, comprising a polymerization step of polymerizing a reactive composition containing a cross-linking agent (b2) to obtain a hydrous gel containing the cross-linked polymer (A2). 2. The water absorbent resin composition according to claim 1, wherein the reactive composition contains a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) upon hydrolysis. Production method. The content of the reactive decomposition product in the reactive composition is 1 part by mass with respect to the total 100 parts by mass of the content of the water-soluble vinyl monomer (a1) and the content of the vinyl monomer (a2). 3. The method for producing a water-absorbing resin composition according to claim 2, wherein the amount is 70 parts by mass or less. 4. The method for producing a water absorbent resin composition according to any one of claims 1 to 3, wherein the number average molecular weight of the reactive decomposition product is 50 or more and 500,000 or less. A shredding step of shredding the hydrous gel to obtain a particulate hydrous gel;
and a surface cross-linking step of surface-crosslinking the water-containing gel obtained in the shredding step,
The method for producing a water absorbent resin composition according to any one of claims 1 to 4, wherein in the shredding step, the reactive decomposition product is kneaded with the hydrous gel. Polymerizing a monomer composition containing a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) by hydrolysis and a crosslinking agent (b3) to obtain a crosslinked polymer (A1) A polymerization step of obtaining a hydrous gel containing
A shredding step of shredding the hydrous gel to obtain a particulate hydrous gel;
and a surface cross-linking step of surface-crosslinking the water-containing gel obtained in the shredding step,
In the shredding step, the crosslinked polymer (A1) having the water-soluble vinyl monomer (a1) and the crosslinking agent (b1) as structural units is irradiated with electromagnetic waves to decompose the crosslinked polymer (A1). A method for producing a water absorbent resin composition, wherein the reactive decomposition product is kneaded with the hydrous gel. 7. The method for producing a water absorbent resin composition according to claim 6, wherein the reactive decomposition product has a number average molecular weight of 50 or more and 500,000 or less.